Is there sufficient light in the hallway? Please share your opinion

If the financial aspect doesn't matter, I would also make 3 windows... unless you are somehow situated on a slope where people can then look completely into the hallway

Or you treat the storage room to a nice south-facing window and a glass door.

We already had the idea with the glass door. It will surely help, maybe not as much as additional skylights.

Would it look bad to put 2 windows only above the staircase? That would at least be enclosed by the gallery railing and might also look quite good?

I think either two above the stairs or all three windows would look good.

North-facing windows have a negative energy balance, if the heart is not attached to three, I would take two.

So we have a skylight upstairs and a small window for the stairs downstairs. During the day everything is bright enough.

So we have a skylight above and a small window for the stairs below. During the day, everything is bright enough.

Ok, good to know. Although the window below looks quite large in your case, we only have a very small one (1 x 0.76) in the hallway, so we would like the double casement windows above the stairs. We have now decided on two 65s, which are to be placed above the stairwell (U-stairs).